CLIMATE change has contributed far more to high crop yields in the US over the past two decades than expected. This indicates that improvements in farming practices have had less effect than thought, so target yields could be harder to meet in the future.

Crop scientists know that cooler temperatures often lead to bumper crop yields and hotter weather can slash them. But constant improvements in fertilisers and crop varieties have improved yields even in regions where the local temperature has risen. This has largely masked the sensitivity of crops to temperature change. Previous studies have not …